The word epigenetics means things imposed “on top of genetics”.
But what sort of things?
Imagine a white mouse breeds with a black mouse – say you get three
white babies and three black babies. That’s
genetics. We can explain that. The black babies inherited a gene encoding the
ability to make the pigment melanin, the others got a defective gene, so they
are white.
But what if you get some stripey mice like zebras? How do you explain that? All parts of the mouse have the
gene that can make black fur but the blackness only occurs in some places.
Think of dalmatian dogs, or of giraffes or leopards.
- Epigenetics is about turning genes on or off.
- It’s also about doing this stably; a leopard doesn’t
change its spots even if it sheds its fur each year.
- So epigenetics is about stable cellular memory that
persists after cell division and, in some cases, even through sexual
reproduction.
- Epigenetics, then, concerns the mechanisms that make
organisms or parts of organisms look different, despite the fact they have
the same genes and are in the same environment.
Epigenetics is
the study of heritable changes in gene activity which are not caused by changes
in the DNA sequence.
MORE EXAMPLES !!
- If you've seen even a few fictional portrayals of twins, you've probably noticed that the presentation tends to lean toward one extreme or the other. Either the twins are eerily alike (such as the little girls in "The Shining") or remarkably different (such as the dominant and submissive twin gynecologists in "Dead Ringers"). When two human beings look so similar, the things that make them different are just as perplexing as those that make them alike.
- One example of an epigenetic change in eukaryotic biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. In other words, as a single fertilized egg cell – the zygote – continues to divide, the resulting daughter cells change into all the different cell types in an organism, including neurons, muscle cells, epithelium, endothelium of blood vessels, etc., by activating some genes while inhibiting the expression of others.
The Future of Epigenetics
- While turning off aging and fine-tuning the human genome are pretty awe-inspiring possibilities, epigeneticists are far more interested in discovering ways to treat epigenetic diseases.
- As some cancers occur due to the deactivation of tumor-suppressing genes, researchers have worked to develop medications that reactivate them. The drug azacitidine, for instance, treats leukemia in this manner.
- Finding just the right parts of the epigenome to treat, however, can be like finding a needle in a haystack. And once researchers find the areas they want to affect, epigenetic drugs aren't all that specific. They might succeed in blocking or unblocking the genes they wanted to treat, but also affect other genes, resulting in potentially dangerous side effects.
- Stem cells are also of key interest to epigeneticists. By studying the epigenetic changes that determine how cells develop, it may eventually become possible to dictate what tissue type a stem cell will develop into.
